(1) Field of the Invention
The present invention relates to an image forming apparatus based on electrophotography, such as a copier, printer, facsimile machine or the like, more detailedly relating to an image forming apparatus which supplies toner to a static latent image formed on a photoreceptor drum, transfers a developed toner image to a recording medium and fuses the unfixed toner image by irradiation of laser light to fix the toner image to the recording medium.
(2) Description of the Prior Art
Image forming apparatuses (e.g., printers and the like) using the electrophotographic technique, include a fixing device that fix the toner image formed on the recording medium (paper) to the paper by thermally fusing the toner image. As this fixing device, patent document 1 has disclosed a fixing device that uses laser light for fixing.
According to patent document 1 (Japanese Patent Application Laid-open H07-191560), use of a multiple number of laser beams to heat the unfixed toner compensates for insufficient fixing performance of a single laser beam configuration and enables improvement in fixing performance. This makes it possible to use inexpensive low-power laser light devices, hence provide an image forming technology with a simplified configuration of the whole apparatus.
As a fixing method that enables efficient fixing of toner without use of waste energy, a flash lamp type fixing device for image forming has been disclosed in patent document 2 (Japanese Patent Application Laid-open 2006-258853), with which the power for fixing is appropriately controlled in accordance with the toner concentration in the developing hopper.
The fixing device of patent document 1 performs fixing by controlling the laser light intensity based on the value detected by a temperature detector. However, since the toner is thermally fused instantly by the laser light, the temperature detected by the temperature detector is not the actual temperature of the toner during its being heated. That is, the laser light intensity is controlled based on the temperature of the toner after it has been heated and fused. As a result, this method cannot achieve correct feedback control and entails the problem that the power of the laser source during irradiation of laser light is consumed wastefully.
Further, since toner is a material that fuses as absorbing light and generating heat by itself, the power (energy) of the light source to be needed for laser irradiation differs depending on the absorptivity of light by the toner and the weight of the toner (the weight of the toner image adhering to the recording medium before fixing). Accordingly, it is necessary to use the energy for irradiation of laser light efficiently, taking into account the toner concentration, the weight of the unfixed toner image and the like even if the print coverage is unvaried. In the fixing device of patent document 2, the energy for irradiation of laser light is used without taking into account any factor of the unfixed toner adhering on the recording medium before fixing, so that there is the problem that waste energy is consumed when the toner is irradiated with laser light.